Until the mid-1980s, the accepted treatment for atherosclerosis, i.e., narrowing of the coronary artery(ies) was coronary by-pass surgery. While effective and having evolved to a relatively high degree of safety for such an invasive procedure, by-pass surgery still involves serious potential complications and in the best of cases an extended recovery period.
With the advent of percutaneous transluminal coronary angioplasty (PTCA) in 1977, the scene changed dramatically. Using catheter techniques originally developed for heart exploration, inflatable balloons were employed to re-open occluded regions in arteries. The procedure was relatively non-invasive, took a very short time compared to by-pass surgery and the recovery time was minimal. However, PTCA brought with it another problem, elastic recoil of the stretched arterial wall which could undo much of what was accomplished and, in addition, creation of the iatrogenic disease known as restenosis, the re-clogging of the treated artery. Another problem associated with PTCA is the formation of intimal flaps or torn arterial linings which can collapse and occlude the blood conduit after the balloon is deflated.
To reduce the partial or total occlusion of the artery by the collapse of the arterial lining and to reduce the chance of thrombosis or restenosis, a stent may be implanted in the artery to keep the artery open. Drug delivery stents have reduced the incidence of in-stent restenosis, which has plagued interventional cardiology for more than a decade.
An alternative to a drug-delivery stent is a drug coated balloon (DCB). A coating containing a drug is formed on the exterior of a balloon. When the balloon is inflated, and the balloon walls contact the vessel walls, the drug is released. The challenges facing the preparation of such coated expandable devices include designing a coating that remains substantially intact during expansion which then delivers the drug to the vessel walls during the procedure. In practice, the majority of the drug is released from the surface of the balloon during its inflation, which may be a few seconds to a few minutes. The challenges in designing such a balloon coating differ from those of designing a coating for a stent or other implantable device which is designed to release the drug over a time period of days, weeks, or even months.
If the coating flakes off a DCB, the coating may present an embolic hazard. This is particularly a concern since many of the drugs that may be useful for delivery via DCB are hydrophobic and dissolve slowly in the bloodstream. Particles or fragments of a coating released from the DCB could produce an embolism if the particle or fragment is larger than the diameter of the vessel. Although drugs will eventually dissolve in vivo, a particle of a hydrophobic drug could potentially present an embolic hazard because the in vivo dissolution or disintegration is slow.
The current invention is directed to methods of coating expandable medical devices, such as catheter balloons, and to the devices themselves that have been so coated. The present invention addresses potential embolic hazards with hydrophobic drugs.